This proposal deals with the demonstration of surface phenomena occurring on cells within the central nervous system (CNS) relevant to the mechanism by which components of the immune system are recruited to the CNS during autoimmune demyelination. These might have significance to the understanding of the pathogenesis of the lesion in multiple sclerosis (MS), a disease in which autoimmunity to myelin antigens is suspected. The hypothesis to be tested herein is that prior to the initial attack or relapses, changes are expressed at the blood-brain-barrier on the membranes of astroglial and endothelial cells in response to components of the immune system and/or specific antigens. It is believed that the changes are the primary orchestrating events in a cascade of immunologic reactions which culminate in the destruction of myelin. This hypothesis will be tested with a series of experiments focused on organized cultures of CNS tissue exposed to a battery of immunologic agents (e.g. lectins, interferon, serum factors, sensitized T cells), and the subsequent membrane events observed on the surface of the principle macrophage in this system, the astrocyte. These events will be monitored by light and electron microscopy using morphology and immunocytochemistry. The demonstration of Ia (Class II MHC, I-region associated) antigen, a primary requirement for the presentation of antigen to T cells, and the presence of antigen on the surface of astrocytes will be a major goal. Ia expression and antigen presentation will be examined in the presence of both humoral and cellular factors, in particular myelin basic protein-sensitized T cell lines. A syngeneic system (SJL mouse CNS tissue tested with SJL serum and cells) in combination with monoclonal antibodies of the appropriate (H2s) haplotype, will be used in most cases except those where heterologous samples (MS cells and sera) are under test. Immunocytology will also be applied in the analysis of receptor-mediated myelin phagocytosis using CNS cultures as the target tissue. Attempts will be made to adapt an existing technique on the culture of bovine CNS endothelial cells to human CNS tissue on which Ia expression and antigen-presentation will be examined. These in vitro experiments will be conducted alongside others on in vivo material and at all times, the observed changes will be referred back to MS lesions. Analysis of the initiating events in autoimmune demyelination, particularly Ia expression, might have therapeutic import for MS and other autoimmune diseases in which anti-Ia treatment is a possibility.